1. Field of Invention
The present invention relates to a method and system for thin film deposition, and more particularly to a system for improving the gas distribution of metal layers formed from metal precursors in uniform, center-enhanced, and edge-enhanced profiles.
2. Description of Related Art
The introduction of copper (Cu) metal into multilayer metallization schemes for manufacturing integrated circuits can necessitate the use of diffusion barriers/liners to promote adhesion and growth of the Cu layers and to prevent diffusion of Cu into the dielectric materials. Barriers/liners that are deposited onto dielectric materials can include refractive materials, such as tungsten (W), molybdenum (Mo), and tantalum (Ta), that are non-reactive and immiscible in Cu, and can offer low electrical resistivity. Current integration schemes that integrate Cu metallization and dielectric materials can require barrier/liner deposition processes at substrate temperature between about 400° C. and about 500° C., or lower.
For example, Cu integration schemes for technology nodes less than or equal to 130 nm can utilize a low dielectric constant (low-k) inter-level dielectric, followed by a physical vapor deposition (PVD) Ta layer or a TaN/Ta layer, followed by a PVD Cu seed layer, and an electro-chemical deposition (ECD) Cu fill. Generally, Ta layers are chosen for their adhesion properties (i.e., their ability to adhere on low-k films), and Ta/TaN layers are generally chosen for their barrier properties (i.e., their ability to prevent Cu diffusion into the low-k film).
As described above, significant effort has been devoted to the study and implementation of thin transition metal layers as Cu diffusion barriers, these studies including such materials as chromium, tantalum, molybdenum, and tungsten. Each of these materials exhibits low miscibility in Cu. More recently, other materials, such as ruthenium (Ru) and rhodium (Rh), have been identified as barrier layers since they have been found to behave similarly to conventional refractory metals. However, the use of Ru or Rh can permit the use of only one barrier layer, as opposed to two layers, such as Ta/TaN. This observation is due to the adhesive and barrier properties of these materials. For example, one Ru layer can replace the Ta/TaN barrier layer. Moreover, current research is finding that the one Ru layer can further replace the Cu seed layer, and bulk Cu fill can proceed directly following Ru deposition. This observation is due to good adhesion between the Cu and the Ru layers.
Conventionally, barrier layers can be formed by thermally decomposing a metal precursor, such as a ruthenium carbonyl precursor, in a thermal chemical vapor deposition (TCVD) process. In low-pressure TCVD systems, the flow of precursor gas is influenced by radial diffusion after the precursor gas leaves a gas distribution system. Consequently, the barrier layer formed on a dielectric material or substrate typically has a center-enhanced dome profile, even when the flow of precursor gas out of the gas distribution system is uniform.
One solution to the forgoing problem is to install a vapor distribution plate at the outlet of a gas distribution system that has more orifices around the edge region of the plate compared to the central region to create higher precursor gas flow through the edge region, i.e., edge-enhanced flow. However, if any process parameter such as pressure, temperature, precursor-type, or gas flow rate change, the system may then require a re-designed vapor distribution plate to accomplish a similar gas flow profile that achieves uniform thickness for a barrier layer formed on substrate. In addition, the vapor distribution plate is fixed in the system and not easily and/or quickly replaceable, such that the system cannot be easily changed to accommodate process parameter changes or to accomplish uniform flow or center-enhanced flow in the event that edge-enhanced flow is not desired.
There is thus a need for a vapor distribution system in which the precursor gas flow can be controlled and changed to accommodate process parameter changes or to switch from edge-enhanced to uniform to center-enhanced flow, as desired, and that does not rely solely upon changing the orifice pattern in the vapor distribution plate to accomplish flow control.